playback: fix error 404 when seeking before start of segment (#4276) (#4533)

Fixes #4276
Replaces #4533

Author: aler9

internal/playback/muxer_fmp4.go

@@ -6,6 +6,7 @@ import (
 
 	"github.com/bluenviron/mediacommon/v2/pkg/formats/fmp4"
 	"github.com/bluenviron/mediacommon/v2/pkg/formats/fmp4/seekablebuffer"
+	"github.com/bluenviron/mediamtx/internal/recordstore"
 )
 
 const (
@@ -156,26 +157,20 @@ func (w *muxerFMP4) innerFlush(final bool) error {
 		}
 	}
 
-	if part.Tracks != nil {
-		part.SequenceNumber = w.nextSequenceNumber
-		w.nextSequenceNumber++
-
+	// no samples to write
+	if part.Tracks == nil {
+		// if no samples has been written before, return an error
 		if w.init != nil {
-			err := w.init.Marshal(&w.outBuf)
-			if err != nil {
-				return err
-			}
-
-			_, err = w.w.Write(w.outBuf.Bytes())
-			if err != nil {
-				return err
-			}
-
-			w.init = nil
-			w.outBuf.Reset()
+			return recordstore.ErrNoSegmentsFound
 		}
+		return nil
+	}
 
-		err := part.Marshal(&w.outBuf)
+	part.SequenceNumber = w.nextSequenceNumber
+	w.nextSequenceNumber++
+
+	if w.init != nil {
+		err := w.init.Marshal(&w.outBuf)
 		if err != nil {
 			return err
 		}
@@ -185,9 +180,22 @@ func (w *muxerFMP4) innerFlush(final bool) error {
 			return err
 		}
 
+		w.init = nil
 		w.outBuf.Reset()
 	}
 
+	err := part.Marshal(&w.outBuf)
+	if err != nil {
+		return err
+	}
+
+	_, err = w.w.Write(w.outBuf.Bytes())
+	if err != nil {
+		return err
+	}
+
+	w.outBuf.Reset()
+
 	return nil
 }
 

internal/playback/muxer_mp4.go

@@ -5,6 +5,7 @@ import (
 
 	"github.com/bluenviron/mediacommon/v2/pkg/formats/fmp4"
 	"github.com/bluenviron/mediacommon/v2/pkg/formats/pmp4"
+	"github.com/bluenviron/mediamtx/internal/recordstore"
 )
 
 type muxerMP4Track struct {
@@ -24,8 +25,9 @@ func findTrackMP4(tracks []*muxerMP4Track, id int) *muxerMP4Track {
 type muxerMP4 struct {
 	w io.Writer
 
-	tracks   []*muxerMP4Track
-	curTrack *muxerMP4Track
+	tracks     []*muxerMP4Track
+	curTrack   *muxerMP4Track
+	hasContent bool
 }
 
 func (w *muxerMP4) writeInit(init *fmp4.Init) {
@@ -73,6 +75,8 @@ func (w *muxerMP4) writeSample(
 		ptsOffset = 0
 	}
 
+	w.hasContent = w.hasContent || dts >= 0
+
 	w.curTrack.Samples = append(w.curTrack.Samples, &pmp4.Sample{
 		PTSOffset:       ptsOffset,
 		IsNonSyncSample: isNonSyncSample,
@@ -93,6 +97,10 @@ func (w *muxerMP4) writeFinalDTS(dts int64) {
 }
 
 func (w *muxerMP4) flush() error {
+	if !w.hasContent {
+		return recordstore.ErrNoSegmentsFound
+	}
+
 	h := pmp4.Presentation{
 		Tracks: make([]*pmp4.Track, len(w.tracks)),
 	}

internal/playback/on_get.go

@@ -64,9 +64,9 @@ func seekAndMux(
 
 		m.writeInit(firstInit)
 
-		segmentStartOffset := start.Sub(segments[0].Start)
+		segmentStartOffset := segments[0].Start.Sub(start) // this is negative
 
-		segmentDuration, err := segmentFMP4SeekAndMuxParts(f, segmentStartOffset, duration, firstInit, m)
+		segmentDuration, err := segmentFMP4MuxParts(f, segmentStartOffset, duration, firstInit, m)
 		if err != nil {
 			return err
 		}
@@ -90,7 +90,7 @@ func seekAndMux(
 				break
 			}
 
-			segmentStartOffset := seg.Start.Sub(start)
+			segmentStartOffset := seg.Start.Sub(start) // this is positive
 
 			var segmentDuration time.Duration
 			segmentDuration, err = segmentFMP4MuxParts(f, segmentStartOffset, duration, firstInit, m)